Manufacturers typically design and assemble conventional globe style control valves to receive a specific type of seat ring, which may be a threaded seat ring or a clamped seat ring. These seat rings, which cooperate with a valve control element such as a valve plug to control fluid flow through the valve, are typically inserted into a cylindrical cavity formed within the valve body. The seat ring is usually separate from the balance of the valve body so that the seat ring can be replaced.
Each type of seat ring tends to have certain advantages and disadvantages. For example, clamped seat rings typically require a separate gasket beneath the seat ring in order to prevent or minimize fluid leakage. On the other hand, threaded seat rings may suffer certain alignment and seal problems, placing a higher premium on maintaining proper tolerances when machining the screw threads in the body and on the seat ring itself.
Because the construction and method of attachment of threaded seat rings and clamped seat rings differ significantly from one another, manufacturers design and construct the valve body to accept only the selected seat ring type. The differences in the two types of valve bodies necessarily prevent one type of valve body from receiving the other type of seat ring. These fundamental differences in the construction of the valve bodies require manufacturers to maintain extra production lines, and require distributors to maintain an inventory of valve bodies for threaded seat rings and valve bodies for clamped seat rings.